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Microarrays and nanoarrays are important commercial developments. Patterned arrays of molecules and in particular biomolecules and biological species, such as oligonucleotides, proteins, virus particles, and cells (eukaryotic and prokaryotic), have been utilized as powerful tools in a variety of biological and interdisciplinary studies. For example, microarrays, in particular, have led to significant advances in many areas of biological and medical research (1). With the advent of powerful new nanolithographic methods, such as dip-pen nanolithography (DPN) printing or patterning (2), there is now the ability for reducing the feature size in such arrays to their physical limit, the size of the structures from which they are made of and the size of the structures they are intended to interrogate (3). Such massive miniaturization not only allows one to increase the density of combinatorial libraries, increase the sensitivity of such structures in the context of a biodiagnostic event, and reduce the required sample analyte volume, but also allows one to carryout studies not possible with the more conventional microarray format.
In order to realize the full potential, including commercial potential, of microarrays and nanoarrays, including biological arrays, the direct deposition of species, molecules, biomolecules using nanolithograhpic techniques (e.g. DPN printing) needs to be as routine and robust as possible. Currently, some applications of DPN printing can be limited to the use of the single component arrays, of either a single oligonucleotide sequence or a given protein. Other applications are not so limited. The ability to make multi-component arrays is dependant on the ability to directly deposit multiple biological molecules simultaneously through DPN printing. Previous advances in this area have been made, but needs yet exist, particularly for commercial applications. One potential limitation is the chemical modification of a tip such as an AFM tip for reproducible tip coating. Different biomolecules may require a specific modification, which can lead to compatibility issues. The second is in the context of parallel DPN printing. Biological molecules can have different transport properties, which can lead to heterogeneous surface features from tip-to-tip, and in some cases, cannot be deposited at all. Finally, denaturation and loss of biological activity can be an issue. In order to bypass these potential limitations, a method that can equalize the transport rates while still preserving the biological activity of the molecules is desirable.